C / C++ / MFC

class cwindow
{
  cwindow(HWND hwnd) // constructor
  {
    SetWindowLong(hwnd,GWL_USERDATA,reinterpret_cast<LONG>(this));
  }
 
  static LRESULT CALLBACK stub_WindowProc(
    HWND hwnd,
    UINT uMsg,
    WPARAM wParam,
    LPARAM lParam)
  {
    cwindow object=reinterpret_cast<object*>(GetWindowLong(hwnd,GWL_USERDATA));
    return object->WindowProc(hwnd,uMsg,wParam,lParam);
  }
 
  LRESULT CALLBACK stub_WindowProc(
    HWND hwnd,
    UINT uMsg,
    WPARAM wParam,
    LPARAM lParam) // the "real" window proc
  {
    ...
  }
};